The invention relates to a locking apparatus for upper and lower molds of a press.
The press is a widely used machine for making various industrial products. For instance, during package stage of semiconductor die, the press has been used together with transfer molds to effect the package of the semiconductor die.
It is well known in the arts that a top platen and bottom platen are provided in the press. The top platen accommodates the upper mold, e.g. transfer mold, and the bottom platen accommodates the lower mold. At the last stage of production of the product, the upper and the lower molds are moved toward each other relatively by operation of press such that they closely match against each other, i.e. a press-match condition. In general, the top platen together with the upper mold is arranged to be stationary and the lower platen together with the lower mold is pushed upward by mechanism of the press to reach the final match-press condition.
The upward movement (stroke) of the lower mold is divided into two different stages which includes a higher-speed lower-pressure long stroke (first stroke) and a lower-speed higher-pressure short stroke (second stroke). At the end of first stroke of operation, the lower mold is only in contact with the upper mold without exerting a strong pressing force to the upper mold. It is the second stroke of the operation which only drives the lower mold by a very short distance and exerts an extreme large force to closely press the molds together. The operation of second stroke of the lower mold is also referred as locking of the upper and lower molds of a press.
In the conventional press machine, the mechanisms performing the locking operation includes well known hydraulic direct-drive type, mechanical crankshaft-drive type, or complex combination of hydraulics and crankshaft drive. However, those well known arts, more or less, experience some drawbacks, i.e. oil leakage, un-expected fluctuation of pressing force, non-uniformity of friction detriment of the crankshaft part after a period of operation, releasing of the pressing force.
To overcome the drawbacks of the conventional approach, the invention provides a locking apparatus which easily applies a desired pressing force and the pressing force may be released also easily by a simple mechanism.
Another object of the invention is to provide a locking apparatus which has smaller size, simple and effective mechanism.